As communication techniques and applications become more and more attractive and important with view to mobile devices, the need for compact antennas increases accordingly. The size of such antennas compared to stationary solutions—is a significant issue. Moreover, properties like directional characteristics are of importance with respect of desired functions.
Concerning the field of vehicle communication, like communication from a car to another car, specific requirements have to be fulfilled with a respective antenna device which for example is an optimised radiation profile in a horizontal direction.
Regarding a more specific technical field of mine vehicles, a vehicle-to-vehicle communication is even more important for providing kind of proximity warnings and thus improved safety for e.g. persons or vehicles in a given area.
Surface mines and similar sites or areas are generally operated by means of a large number of vehicles and staff.
Some of the vehicles may be exceedingly large, heavy, and difficult to control. It has been proposed to use GNSS-devices (GNSS=global navigation satellite system, such as GPS) on board of vehicles and other objects, such as cranes, to generate proximity warnings in order to reduce the risk of collisions between vehicles. Such a system is e.g. described in WO 2004/047047 based on devices mounted to the objects. Each device comprises a GNSS receiver, a control unit deriving positional data using the signal of the GNSS receiver, a radio circuit for wireless exchange of the positional data with the other devices, and an output device for outputting proximity warnings. Such systems allow the driver of a vehicle to obtain information on some of the obstacles nearby. Another improved such system is known from WO 2010/142046 A1.
Corresponding to the use with automobiles, such communication device (radio circuit) needs to be designed and arranged at the respective moving vehicle such that a signal sent from that device propagates in a way to be suitably received by another such vehicle or central processing unit. For typical vehicle-to-vehicle or vehicle-to-receiving unit communication the signals are to be sent in substantially horizontal direction and/or the receiver comprises a respective preferred horizontal receiving direction.
Kaufmann, T. et al. propose in “Low-Profile Magnetic Loop Monopole Antenna Based on a Square Substrate-Integrated Cavity”, International Journal of Antennas and Propagation, Volume 2015, Article ID 694385, a low-profile monopole antenna having a square substrate-integrated cavity radiating through apertures in its four side walls. Such antenna fulfils the crucial requirement of an omni-directional radiation pattern with maximum in or close to the substrate plane.
Promising geometries to achieve these requirements can be based on low-profile resonant cavities, with fringing fields from thin apertures forming equivalent magnetic currents as described therein. The antenna is a square patch monopole completely integrated in a substrate using shorting vias. Compared to prior art, this antenna combines compactness and low profile, while the proposed approach provides a new perspective to planar monopole antenna design: instead of being considered a loaded monopole, the structure is interpreted as an opened rectangular cavity. The radiation originates from four regions along the side walls, which effectively creates a square-magnetic current loop. This results in an equivalent electric monopole antenna that is radiating omni-directionally, is compact, is of low-profile and is robust to tolerances.
However, such solution focuses on omni-directional radiation for only one defined frequency (5.8875 GHz in the DSRC band), wherein (simultaneously) different frequency bands are typically used for vehicle communication purpose. In addition, as for integration in a moving vehicle receiving and processing of a GNSS signal is required as well, the problem of suitable combination of such devices or signal still remains.
WO 02/080307 A1 proposes an antenna device comprising two or more antennas in a single housing/radome. A first top loaded, monopole antenna is nested within a ground plate and a top plate of a second top loaded, monopole antenna.
Additionally, a further microstrip antenna may be positioned on top of the second monopole antenna. The first antenna may be designed to transmit and receive in the AMPS bandwidth, the second antenna in the PCS bandwidth and the microstrip antenna in the GPS bandwidth. Due to the design of the combined antennas the overall size and complexity of the antenna device is quite disadvantageous with corresponding negative impact on flexibility of mounting or integrating the device onto or into a moving vehicle.